Heat sealable and peelable films are generally made from one or more polymeric resins. The resulting characteristics of a heat sealable and peelable film depend largely upon the type of resins used to form the film. For example, ethylene vinyl acetate (EVA) and ethylene methyl acrylate (EMA) copolymers provide excellent heat sealing properties. However, the seals produced with these copolymers are such that separation usually cannot be achieved without damage to the film, i.e., the seal is a “hard seal”. To alleviate this problem, polybutylene is mixed with an EVA polymer to produce a heat sealable and peelable film, i.e., the seal is a “frangible seal”. Although the peelability of the film is improved, this blend lacks good hot tack strength and the peelable film has some unpleasant odor due to the presence of EVA. In addition to using polybutylene, some ionomers, such as SURLYN® ionomer resin (a copolymer of ethylene and methacrylic acid), is mixed with EVA to produce a heat sealable and peelable film. While the film is peelable, it causes stringiness or “angel hair” upon separation of the film. Moreover, ionomers are generally expensive and may have some odor as well.
Oriented polypropylene (OPP) laminates are commonly used for packaging, e.g., forming pouches by fin- or lap-seals (to form the tube of the pouch) and end-seals (to close the pouch on both ends). Lap seals are formed by overlapping the inside (interior) layer (i.e., the sealant layer) of the structure and the outside (exterior) surface of the structure and heat sealing them. Fin seals are formed when the inside (sealant) surfaces of the structure meet and seal against themselves, typically in the back center of the bag. Lap seals provide material saving, compared to fin seals, because of not having to create folds.
Strong sealants to polypropylene (PP)-based films such as elastomers and plastomers provide high hermetic seals but lack peel seal attributes.
WO 2014/100386 teaches a combination of peel-seal (frangible seal) and lock-up seal (hard seal) of propylene-based plastomers or elastomer (PBPE) resin in a multi compartment pouch format but in all cases by sealing two sealant layer surfaces. It does teach packaging formats with fin seals.
Of continuing interest to the packaging industry is a package with both a peelable end seal (for consumer convenience) and a non-peelable lap seal (for hermetic sealing during handling and transportation). Such a package is a challenge for the typical sealants used in oriented PP-based laminates. Such sealants, e.g., PBPE, in a pouch format generally provide non-peelable seals for the end-seals and the lap-seals.